Cam overlap, how important is this?
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From: Cleburne, Tx.
Cam overlap, how important is this? I have my eyes set on a cam for my N/A 370 build. I was talking with a guy at work, and he told me it had 90 degree's of overlap. Is that bad or good? And why.
Add the intake and exhaust durations
Divide the results by 4
Subtract the LSA
Multiply the results by 2
Keep in mind most cam specs are given at .050 and you need seat to seat times to calculate correctly..
The easiest way is to add the intake opening time to the exhaust closing time and VIOLA!!!. See your cam card....
Note: just about everybody on here you see figures it at .050 and gets - numbers to + numbers in the teens usually..... but not true overlap.... I guess it can be used as a reference though ......
BUT YEA 90* IS REDICULOUS..... 90* is an ALL out race cam....
Divide the results by 4
Subtract the LSA
Multiply the results by 2
Keep in mind most cam specs are given at .050 and you need seat to seat times to calculate correctly..
The easiest way is to add the intake opening time to the exhaust closing time and VIOLA!!!. See your cam card....
Note: just about everybody on here you see figures it at .050 and gets - numbers to + numbers in the teens usually..... but not true overlap.... I guess it can be used as a reference though ......
BUT YEA 90* IS REDICULOUS..... 90* is an ALL out race cam....
Last edited by SOMbitch; Aug 16, 2010 at 03:42 PM.
Overlap is when both valves are open at the same time. That's how you get the inversion that causes the lope and not to mention bucking just off of idle. More overlap, more bucking and tuning problems.
Though a good tuner can smooth it out pretty good.
If you have to pass smog, it's best to have 0 or negative overlap.
Though a good tuner can smooth it out pretty good.
If you have to pass smog, it's best to have 0 or negative overlap.
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To get the overlap I use the average of the intake and exhaust durations and subtract the LSA x 2. The bigger the number the more overlap. Negative numbers make good blower cams.
